Graduation Year

2022

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Sarina J. Ergas, Ph.D.

Committee Member

Mauricio E. Arias, Ph.D.

Committee Member

Qiong Zhang, Ph.D.

Committee Member

John N. Kuhn, Ph.D.

Committee Member

James S. Bays, M.S.

Keywords

High Solids Anaerobic Digestion, Hybrid Constructed Wetlands, Methane, Nitrogen, Organic Matter

Abstract

Biochar is an inexpensive and environmentally friendly carbonaceous pyrolysis byproduct with a high surface area, pore volume, and adsorption capacities for inorganic and organic compounds. The goal of this dissertation is to evaluate the feasibility of biochar application in biological treatment systems for enhanced waste management. Three major objectives guided this research to provide a compressive understanding of biochar enhancement effects on biological treatment systems for contaminant removal, energy recovery, and environmental impacts as well as essential factors influencing biochar production and properties.

In Objective 1 a low-cost hybrid Constructed Wetland (CW) system modified with biochar/zeolite was developed for enhanced landfill leachate treatment (Chapter 2). Leachate percolating through landfills contains high concentrations of ammonia, recalcitrant organic matter, and heavy metals, which can interfere with treatment processes in wastewater treatment plants. Hybrid CWs, consisting of a Vertical Flow (VF) tank followed by a Horizontal Flow (HF) tank, are cost-effective technologies for onsite leachate treatment. Two mesocosm hybrid CWs without (Control-CW) and with adsorbent addition (Adsorbent-CW) were constructed at the Southeast Hillsborough County landfill in Florida. The Control-CW was filled with conventional gravel medium, while the Adsorbent-CW was amended with 10% (v/v) of zeolite in the VF tank and 13% (v/v) of biochar in the HF tank. Both systems were planted with cattail (Typha spp) and cordgrass (Spartina) and operated at varying hydraulic retention times (11d, 7d, and 4.5d) for ~2 years. To further enhance denitrification, wood chips (Woodchip-CW) were used as a carbon source in a second HF tank downstream of the Adsorbent-CW on Day 540. Results showed that biochar addition improved organic matter and color removals by effective adsorption from 22-33% to 29-43% and from 0-20% to 6-49%, respectively. Zeolite addition remarkably increased nitrification rates in the Adsorbent-VF by 35-96%, especially under higher ammonia loading conditions. Zeolite addition also reduced free ammonia inhibition to nitrifiers, with concentration lower than 10 mg/L under all hydraulic conditions. Improved plant growth was achieved within Adsorbent-HF, which was likely due to the reduced concentrations of ammonia and heavy metals and enhanced rhizosphere microbial activity. Implementation of the Woodchip-CW significantly reduced nitrate accumulation by releasing organic matter and enhancing denitrification. After addition of the Woodchip-CW, total nitrogen removals of up to 78-80% were achieved.

In Objective 2 the effects of biochar addition on long-term system and environmental performance of High Solids Anaerobic Digestion (HS-AD) of lignocellulosic banana waste was evaluated (Chapter 3). Banana waste (peel, stem, and leaf) with high lignocellulose content is generated in large quantities around the world. HS-AD of lignocellulosic waste can recover energy and reduce its environmental impacts. However, high carbon/nitrogen ratios and low water content in HS-AD can potentially cause system acidification and/or failure. Biochemical methane potential assays with varying biochar dosages (2.5-30%) showed that 10% biochar addition increased methane yields by 7% compared with unamended controls. Long term semi-continuous HS-AD studies, without and with 10% biochar addition, were conducted at varying solids retention times (42, 35, and 28 days). Biochar addition reduced volatile fatty acid accumulation, improved system stability and increased methane production by 20-47%. Specific methanogenic activity assays showed that biochar amended reactors had higher levels of acetate consuming methanogenic activity and lower hydrogen consuming methanogenic activity than controls. This indicates that biochar amendment promotes the activity of acetrotrophic methanogens and facilitates direct interspecies electron transfer. The nutrient content of digestate from HS-AD of banana waste indicated its potential use as a bio-fertilizer. Life cycle assessment results showed that biochar addition to HS-AD resulted in greater environmental benefits in most categories compared with the control, including eutrophication, ecotoxicity, and fossil fuel depletion when biochar was available within a radius of 8,830 km.

In Objective 3 the production of high-quality biochar from lignocellulosic banana waste was investigated (Chapter 4). Banana waste and AD digestate are promising pyrolysis feedstocks for biochar production. Pyrolysis of raw banana waste and digestate from semi-continuous AD reactors was carried out under varying conditions, including pyrolysis temperature and residence time. Results showed that biochar derived from raw banana waste had higher cation exchange capacity and acid adsorption capacities than digested biochars. Increasing pyrolysis temperature from 300℃ to 700℃ decreased biochar yields by 28-53%, decreased cation exchange capacity by 77-95%, and increased acid adsorption capacities by 40-110%. Increasing pyrolysis residence time from 30min to 2h decreased biochar yields at lower temperature (300℃) (P<0.05) and had no significant impacts at higher temperatures (500℃ and 700℃) (P>0.05). Biochar produced from biochar amended HS-AD digestate showed higher acid adsorption capacity than control digestate biochar.

This dissertation comprehensively investigates the combined effects of biochar and zeolite addition to hybrid CWs on contaminant removal from landfill leachate and enhancement effects of biochar on renewable energy recovery from HS-AD of banana waste as well as environmental impacts. To the best of my knowledge, the research conducted in this dissertation has not been carried out previously. Results from this dissertation provide an improved understanding of biochar application in low-cost biological treatment systems for high strength wastewater and lignocellulosic waste disposal. Modified hybrid CW by biochar and zeolite can potentially treat other types of waters, such as waters contaminated by highly recalcitrant organic matter, such as poly-and perfluoroalkyl substances, acid mine drainage with high heavy metal concentrations. The biochar-amended HS-AD can also potentially be used to treat other lignocellulosic waste or high carbon/nitrogen ratio waste, such as corn stalks, rice straw and hulls, and wheat straw.

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